The field of this invention relates to devices that can grip tools and prevent them from falling into a well bore during attempted removal.
In oil field operations, various tools are extremely long and are taken apart joint by joint as they are removed from the well bore. The well bore typically has a blow out preventor through which the tubulars are to be removed. Techniques have been developed to deploy and remove tools in a live well. These devices grip the string in the well bore and seal off the well bore allowing disassembly of a component above the seal. Thereafter, some sort of gripping tool grabs the remaining portion of the assembly that extends in the hole before the lower support is retracted. Once the lower support is retracted, the next joint can be pulled through the blowout preventor and the ram and seal assembly can then be actuated to again support the string and seal off the well bore. The problem arises when the running or gripping tool that is supposed to suspend the string when the support ram is opened does not have a good grip on the string and a release results. Many oil field operators have experienced a loss of equipment downhole when the lower support for the string above the blowout preventor released but the string was not otherwise supported.
Thus, an objective of the present invention is to provide a simple readily installable mechanism for the blowout preventor to prevent loss of equipment for tubulars downhole. The device is self-actuating and permits removal while at the same time catching the string should there be an accidental disconnect at or above the blowout preventor.
In the past, a blowout preventor design involving rams with a series of gripping devices has been used to permit insertion of tubulars into a well bore that is experiencing a blowout. In those conditions, it was desirable to have a mechanism which would keep the downhole tools or tubulars from blowing out of the well after they were inserted beyond the blowout preventor. Accordingly, one prior design employed gripping devices in a blowout preventor which permitted insertion of tubulars into a well blowing out with a feature to automatically prevent them from coming out. Yet despite the existence of this device, numerous large oil field service companies have experienced the unpleasant effects of dropping tools or tubulars in the process of removing them from the well bore.
Accordingly, what has been needed and what this invention provides is a simple economical and reliable technique to prevent losing tubulars and tools downhole during the removal process.
A pair of ram blocks are provided such that when they are actuated hydraulically to move together, they present an opening which has a series of gripping members downwardly biased. Removal of tubulars or tools from the well bore works against the bias to retract the grippers so that removal can be accomplished. However, if there is an accidental release, the bias pushes the grippers toward the tubular or tool to grip it to prevent loss into the well bore. The ram blocks can be retracted for run-in to the well bore.